The removal and disposal of extremely hazardous materials, such as carcinogenic, friable asbestos-containing materials, from building components is of great importance. The removal of such material, while necessary for safety reasons, is, however, an inevitably dangerous process. Removal or abatement processes are also generally regulated by state, local and federal environmental standards, which relate in part to the isolation and decontamination assemblies for such abatement methods.
One known abatement method requires the particularly expensive and time-consuming erection and use at the asbestos removal site of a complete multi-layer isolation and decontamination assembly within the building. This assembly includes a number of separate functional chambers, interconnected airlocks, asbestos removal equipment storage areas, clean rooms with triple flap curtains on each, isolated personnel decontamination showers and constantly operable high capacity HEPA filter systems. This method typically utilizes overlapping polyethylene sheets between the work area and each section of the decontamination chamber. Air moving into the work area responsive to the operation of negative air machines moves through the overlapping sheets. The sheets are arranged to stop contaminated air in the work area from passing out of the work area any time the negative air pressure in the work area is lost. The sheets also prevent positive pressure from occurring in the work area, causing contaminated air from the work area to pass outwardly. This method typically requires constant and precise monitoring of both the interior of the isolation and decontamination assembly to insure that the asbestos fiber concentration level within does not exceed a predetermined level.
Small scale asbestos removal apparatus such as glove bags and the like are also known and generally also require the use of HEPA air filtration systems.
The inventors herein have previously invented an apparatus and method for the safe and effective, large scale removal and disposal of hazardous materials from building components as set forth in U.S. Pat. No. 4,817,644, issued Apr. 4, 1989 to Holmes et al. In that patent, a new and improved apparatus and method for the removal of friable asbestos-containing materials from building components is provided which includes a sheet-like body member and one or more generally elongated, close-ended chutes operatively connected to the body member. In use, the body member is sealed around the building component from which hazardous material is to be removed, and then the hazardous material is moved into the belly of the body member and through the chutes for periodic packaging and disposal. In that method and apparatus, an HEPA negative pressure system is connected to the body member, enabling the constant replenishment of air from the ambient surroundings and preventing collapse of the enclosure as contaminated air from within the enclosure is withdrawn through use of a vacuum source. The vacuum source also includes a HEPA filtering system.
One known HEPA vent filter device comprises a housing having openings in front and back walls, a partition in the housing between the front and back walls defining a framed opening, an extensible wall on the exterior of the housing between the front and back walls, and a HEPA filter pivotally mounted for movement toward and away from the framed opening. See, U.S. Pat. No. 4,963,170, issued Oct. 16, 1990 to Weber et al. When a reduced pressure of a previously determined amount is applied to the pivoting filter, the filtering element is sealed between a knife edge and allows unfiltered air to flow into the work area. Upon loss of negative pressure, gravity causes the filter to rotate to a closed position to filter any reverse airflow. There are various problems with this design. First, this vent filter device is a multi-part construction. This leads to difficulties in manufacture and use. The numerous moving parts are each susceptible to wear, resulting in a typically short life span for the device.
Second, the HEPA filter's life span itself has been found to be very short in this design. In the Weber et al. design, the HEPA filter is susceptible to damage because the filter is sealed between a knife edge. That design requires the operator to remove and package the HEPA filter after each use in order to increase the life span, and such constant removal tends to cause damage to the HEPA filter because of its orientation with respect to the knife edge. The HEPA filter is one of the most expensive parts of the filter device.
Third, the filter device of Weber et al. relies on gravity and pressure to open and close the filter, and thus, it must be positioned upright in order to work properly. If the device is positioned incorrectly, gravity may hold the HEPA filter open at negative pressures. The weight of the HEPA filter makes this design particularly susceptible to such problems.
Thus, there is a need for a filtering system with this design which is capable of repeated, versatile, and efficient use.
Other filtering systems, not known for use in the removal of asbestos or other hazardous materials, are known wherein the filter element is movable from an operative position to a bypass position. See, for example, U.S. Pat. Nos. 4,356,007, issued Oct. 26, 1982 to Bowman, 4,312,645, issued Jan. 26, 1982 to Mavros et al. and 2,992,701, issued Jul. 18, 1961 to White.
Filtering systems wherein a filter panel is used to collect particulate material and thereafter selectively removed are also known, as shown in U.S. Pat. Nos. 3,756,416, issued Sep. 4, 1973 to Wood and 4,217,116, issued Aug. 12, 1980 to Seever. None of these known filtering systems or devices, however, are known to be useful in the removal of asbestos or other hazardous materials or overcome the deficiencies of known filters for that use.